For nearly two years, fans of ABC Family's Pretty Little Liars have been asking the same question: Who is "A?"

They finally got an answer during the shocking Season 2 finale Monday, when Aria Montgomery (LucyHale), Emily Fields (Shay Mitchell), Hanna Marin (Ashley Benson) and Spencer Hastings (TroianBellisario) learned that the villainous character was none other than Mona Vanderwaal, played by JanelParrish.

"A lot of my cast members hadn't seen the episode yet, so when they finally got home last night they all started calling and freaking out," Parrish, 23, told Us Weekly during a phone interview Wednesday. "A couple of them suspected that it was me, and I had to tell them they just had to wait and see."

Keeping the heavily-hyped plot twist under wraps was tough for Parrish, who said she "had so much fun" filming the intense episode.

"I just wanted to be able to tell everyone what I was doing on set and that I was having a great time," she explained. "I couldn't really tell anyone, but it was worth it because I wanted people to be surprised when they saw it."

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Though Mona Vanderwaal was revealed as "A" in Sara Shepard's Pretty Little Liars book series, "the writers always said that things could change [on the show], so I shouldn't get attached to that idea," Parrish told Us.

"I officially found out that [my character is "A"] a week before we filmed the finale when we got the scripts for the table read. Everyone was just so shocked and excited and it was kind of surreal," Parrish said. "For two years I've kind of hoped that's where it was going to go, so when I was sitting there reading the script. it was kind of surreal."

Though her character was being treated for "a personality disorder" at the end of Monday's episode, "in Season 3 we're going to find out a lot more about her motives and why she does what she does," Parrish added.

The unmasking of "A" wasn't the only big twist in Monday's finale: Emily Fields' on-and-off girlfriend Maya St. Germain (Bianca Lawson) was found dead at the end of the episode, though her killer's identity remains a mystery.

"I think that everyone probably has a different idea of who did what," Parrish teased. "I don't think that anyone should be surprised that anyone in that town could be capable of murder."